1. Field of the Invention
The present invention relates to a rotor for an electric motor including a shaft, a lamination parcel and a current distribution element which are mounted on the shaft coaxially with the shaft for joint rotation with the shaft, and an insulating layer that insulates the lamination parcel and the current distribution element from the shaft.
2. Description of the Prior Art
German Publication DE -OS 25 43 549 discloses an electromotor for a hand-held power tool and which can be used, e.g., as a drive motor in drilling and chisel tools. Because in this electric motor the lamination parcel and the current distribution element, which is formed as a commutator, have different inertia moment, different acceleration forces act on the lamination parcel and the current distribution element, in particular during actuation of the electric motor or its braking. These acceleration forces may result in the lamination parcel and the current distribution element rotating in opposite directions. To avoid such opposite rotation, the lamination parcel and the current distribution element of the known electric motor are mounted on the rotor shaft for joint rotation therewith by an intermediate steel pipe separated from the shaft with an insulating layer.
Because the current distribution element is formed of segment-shaped sections each of which cooperates with one rotor pole, alignment of separate sections of the current distribution element with the rotor poles of the lamination parcel in the circumferential direction is necessary. In the known electric motor, the alignment is achieved by using a steel pipe onto which both the lamination parcel and the current distribution element are pressed-on before the steel pipe is connected with the rotor shaft for joint rotation with the shaft, with the insulating layer being provided between the shaft and the steel pipe. The insulating layer can be formed, e.g., as a plastic sleeve glued between the steel pipe and the rotor shaft. The drawback of glue connections consist in that at high motor temperatures, they become destroyed which leads to a damage of an electric motor. It is also possible to form the insulating layer by injection. With this method of forming the insulation layer, first, the steel pipe and the rotor shaft should be secured in a retaining device in which the steel pipe should be so retained against the rotor shaft that a cylindrical clearance is formed between the two parts. The injection of the insulating layer is associated with increased cost associated in part by a need for additional equipment. Furthermore, cooling of the insulating layer consumes a large amount of time.
Accordingly, an object of the present invention is to provide an electric motor and, more specifically, a rotor for an electric motor the insulating layer of which can be economically produced and rapidly and simply connected with the rotor shaft for joint rotation therewith. The insulating layer should further insure a simple alignment of the current distribution element with the lamination parcel and should provide for mounting of the lamination parcel and the current distribution element on the rotor shaft for joint rotation with the shaft. At that, the total weight of the rotor assembly should be a s small as possible.